Code for moving angular servo at specific speed

Davyd · September 9, 2025, 7:09pm

I’ve been tearing my hair out trying to write a code block that will move an angular servo to a specific angle at a specific speed. I need it so I can trigger the movement after a delay to avoid moving parts clashing.

This is what I’ve been working with, based on the documentation, picking my friends brains (who know a bit of python) and even stooping so low as to use ChatGPT (sad face).

import time
import machine
from bbl.servos import ServosController 

servos = ServosController()

servos.set_angle_stepping(2, 90, 10)

def proc(t):
    servos.timing_proc() 
tim = machine.Timer(0) 
tim.init(period.10, mode=Timer.PERIODIC, callback.proc) 

while servos.servos_info_map[0]["step_en"]: 
    time.sleep(0.05) 

tim.deinit()

I know I’m doing something stupid, I just can’t figure out what so would massively appreciate any help

xrk · September 9, 2025, 8:27pm

Have a look at the following CyberBrick MicroPython function, especially the velocity:

github.com/CyberBrick-Official/CyberBrick_Controller_Core

src/app_rc/bbl/servos.py

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          def timing_proc(self):
              """
              Periodically checks and updates the servo motors that are in stepping mode.
          
              This method is called by a timer or main loop to \
                  update the servo positions gradually.
              It calculates the next angle based on the velocity and \
                  sensitivity settings, and applies the PWM duty cycle.
          
              Example:
                  >>> # Call timing_proc in the main loop to update servo positions.
                  >>> servos.timing_proc()
              """
              for servo_idx in range(4):
                  if self.servos_info_map[servo_idx]["step_en"] is False:
                      continue
          
                  c_ang = self.servos_info_map[servo_idx]["c_ang"]
                  s_ang = self.servos_info_map[servo_idx]["s_ang"]
                  velocity = self.servos_info_map[servo_idx]["vel"]

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that is called from timer 0 callback:

github.com/CyberBrick-Official/CyberBrick_Controller_Core

src/app_rc/app/control.py

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          def timer0_callback(self, timer):
              self.motors.motors_period_cb()
          
              for dev in self.d_ch_map:
                  if dev is not None:
                      dev.timing_proc()
          
              if self.tim0_div_cnt == 0:
                  self.servos.timing_proc()

Davyd · September 9, 2025, 8:29pm

I’m sorry, I’m really ignorant of python (or programming in general, very much a late 90s script kiddy). I don’t really understand what you’re telling me or how I could apply it.

Sorry for being a pain

xrk · September 9, 2025, 8:39pm

The message I was trying to convey is that the velocity control is already there in the original MicroPython CyberBrick code stack.

You need step_en for the servo output to be set to True and then you should be able to control servo velocity with vel key. The code will slow down the velocity from max to a lower value while it drives to the new set point of the angular servo.

src/app_rc/bbl/servos.py

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          def set_angle_stepping(self, servo_idx, angle, step_speed=None):
              """
              Sets the servo to move to the target angle using stepping motions.
          
              The servo will gradually move to the target angle \
                  at the specified speed.
          
              Args:
                  servo_idx (int): Index of the servo motor (1 to 4).
                  angle (int): Target angle between 0 and 180 degrees.
                  step_speed (int, optional): \
                      Speed of the movement (0-100). Higher values move faster.
          
              Example:
                  >>> # Set servo 2 to 180 degrees with a step speed of 10
                  >>> servos.set_angle_stepping(2, 180, 10)
              """
              if not 0 <= angle <= 180:
                  print("[servo]Invalid angle, Must be between 0 and 180.")
                  return

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Davyd · September 9, 2025, 8:46pm

I genuinely might be misunderstanding you, but I’m pretty sure I’m aware that vel is already there in the stack.

I’m calling servos.set_angle_stepping(idx, angle, vel) and defining idx (1), angle (180), and vel (20%).

However the issue I think I’m running into is that servos.timing_proc() isn’t getting called meaning that step_en and the current step aren’t being updated for the servo. Without that (I think) nothing will happen.

I think I need a timer that does a callback to timing_proc() to incrementally update things, but I can’t seem to get that to work.

What you’ve linked to looks like the source for the call I’m trying to make.

I just can’t figure out what’s wrong and why step_en never seems to go true or why timing_proc() doesn’t seem to update anything.

As someone who doesn’t know python and can’t program for toffee, I don’t know what my code block is supposed to look like.

xrk · September 9, 2025, 8:47pm

If you are trying to do fully custom code, then mimic the main program entry, as is done in:

github.com/CyberBrick-Official/CyberBrick_Controller_Core

src/app_rc/app/rc_main.py

master

# -*-coding:utf-8-*-
#
# The CyberBrick Codebase License, see the file LICENSE for details.
#
# Copyright (c) 2025 MakerWorld
#

import sys
import machine
import uasyncio
import time
import ulogger

sys.path.append("/app")
if '.frozen' in sys.path:
    sys.path.remove('.frozen')
    sys.path.append('.frozen')


async def master_init():

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This would be the main loop for the receiver side:

github.com/CyberBrick-Official/CyberBrick_Controller_Core

src/app_rc/app/rc_main.py

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          async def control_task():
              EMPTY_DATA = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
              global conf_update_flag
              setting = None
              rc_index = 0
          
              while True:
                  try:
                      if conf_update_flag is True:
                          # Free memory before load file.
                          conf_update_flag = False
                          bbl_controller.reinit()
                          rc_conf = None
                          setting = None
                          gc.collect()
          
                          try:
                              with open('rc_config', 'r') as f:
                                  rc_conf = ujson.load(f)
                                  gc.collect()

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while you also need to run bbl_controller.executor_handle() cyclically as in:

github.com/CyberBrick-Official/CyberBrick_Controller_Core

src/app_rc/app/rc_main.py

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          await uasyncio.gather(control_task(),
                                period_task(),
                                simulation_task(),
                                bbl_controller.executor_handle())

with the main meat being in:

github.com/CyberBrick-Official/CyberBrick_Controller_Core

src/app_rc/app/rc_main.py

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          rc_data = rc_module.rc_slave_data()
          data_parser.set_slave_idx(rc_index)
          
          if rc_index != rc_module.rc_index():
              # Must update config
              conf_update_flag = True
              continue
          
          if rc_data and setting and rc_data != EMPTY_DATA:
              bbl_controller.handler(setting, rc_index, rc_data)

Davyd · September 9, 2025, 8:54pm

I’m not trying to do fully custom code, I’m trying to build a small code block within the Cyberbrick App to do a specific thing. I’m not sure why mimicking the main program entry is the right way to go about things?

I’ve managed to make a code block that can move the servo to a specific angle:

import time
import machine
from bbl.servos import ServosController 

servos = ServosController()

servos.set_angle(1, 180)

time.sleep(5)

servos.set_angle(1, 0)

time.sleep(5)

This will move the servo to 180 degrees, wait 5 seconds, then move it to 0 degrees before waiting another 5 seconds and then ending the script. I built it using the syntax info here: ServosController — MicroPython for CyberBrick V01.00.00.03 documentation

xrk · September 9, 2025, 8:57pm

My bad, I see that you are doing it via CyberBrick app code injection, which I know nothing about, so just ignore my comments above.

Davyd · September 9, 2025, 8:58pm

No worries, I could’ve been a lot clearer. Like I said, programming dunce

xrk · September 9, 2025, 9:03pm

Just a wild guess, but did you try just

servos.set_angle_stepping(1, 180, 10)

(where you set the angle to something else than 90, which is the center)?
The whole Timer0 task should already run in the bg, so IMHO no need for you to explicitly do anything with it:

github.com/CyberBrick-Official/CyberBrick_Controller_Core

src/app_rc/app/control.py

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          self.tracker_low_speed_zone_pctg = [0] * 2
          self.tracker_high_speed_zone_pctg = [0] * 2
          self.high_speed_duration = [1] * 2
          
          self.servos_effect_data_list = [0] * 4
          self.motors_effect_speed_list = [0] * 2
          
          self.adc_deadzone_list = [200] * 6
          self.adc_mid_list = [2048] * 6
          
          self._timer_init()
          
          self.button_handler.long_callback_register(self._button_long_cb)
          self.button_handler.short_callback_register(self._button_short_cb)
          self.button_handler.press_down_callback_register(self._button_press_cb)
          self.button_handler.release_callback_register(self._button_up_cb)
          
          self.key_short_effects_list = [CycleList()] * 4
          self.key_long_effects_list = [CycleList()] * 4
          self.key_down_effects_list = [CycleList()] * 4
          self.key_up_effects_list = [CycleList()] * 4

Davyd · September 9, 2025, 9:06pm

I have tried it setting the angle to 0, 90, 45, 135, and 180 to no joy.

If timer0 is running in the background, how would I use it to trigger servos.timing_proc() at regular intervals?

xrk · September 9, 2025, 9:08pm

Also that is already happening:

github.com/CyberBrick-Official/CyberBrick_Controller_Core

src/app_rc/app/control.py

740f89196


      
          def timer0_callback(self, timer):
              self.motors.motors_period_cb()
          
              for dev in self.d_ch_map:
                  if dev is not None:
                      dev.timing_proc()
          
              if self.tim0_div_cnt == 0:
                  self.servos.timing_proc()

This page really needs some examples to be easier to follow:
https://wiki.bambulab.com/en/makerworld/cyberbrick/ai-advanced-programming

Davyd · September 9, 2025, 9:12pm

Weird, so it should just work when I call servos.set_angle_stepping? Wtf am I doing wrong?

I agree with the need for better examples

xrk · September 9, 2025, 9:20pm

You could try to get some debug info flowing back to you by attaching a REPL terminal via USB to the CyberBrick (e.g. Arduino Lab for MicroPython), so that you can follow on the terminal what it is doing.

Davyd · September 9, 2025, 9:33pm

I’ll try that again, but I’ve been having issues with the board crashing when connected to a debugger. Again, I’m probably doing something wrong, lol

Mangto · September 12, 2025, 3:33am

Hey, you are right, the timing_proc() of each actuator (such as servos, LED and motors) has been called periodically by timer(0) in the background, so in the code block you only need to call the function interface (such as servos.set_angle_stepping(2, 90, 10), so you don’t need to trigger servos.timing_proc() again in the code block.

Mangto · September 12, 2025, 7:06am

I tried using servos.set_angle_stepping() to achieve a specific speed and a target angle, and I tried the following code.

import time
from bbl.servos import ServosController 

servos = ServosController()

servos.set_angle_stepping(2, 90, 10)
time.sleep(1)

servos.set_angle_stepping(2, 0, 10)
time.sleep(1)

servos.set_angle_stepping(2, 180, 10)
time.sleep(1)

But it didn’t work. I eventually discovered that the ServosController module doesn’t use the new method to implement a singleton, unlike the LEDController and MotorsController design, like this:

def new(cls, *args, **kwargs):
if not cls._instance:
cls._instance = super(MotorsController, cls).new(cls)
return cls._instance

This caused the ServosController instance running in the background to become inoperable. I believe this is a bug that CyberBrick engineers will fix soon.

xrk · September 12, 2025, 8:13am

You could try this out yourself by modifying the original CyberBrick codestack files via REPL on your CyberBrick Core. And if that solved the issue, then you could submit a pull-request to Pull requests · CyberBrick-Official/CyberBrick_Controller_Core · GitHub to fix it.